Puppet users - Feb 2012 - Parameterized classes override of parameter

Hi group,

I expect parameterized classes to behave simular to types in relation
to overrides, but obviously this is not the case.
Could someone what is should then expect from overriding an parameterized class.

what I have is:

class dns(dns_servers) {
  file{''/etc/resolv.conf'':
      content => template("dns/resolv.conf.erb")
  }
}

class role::init {
   class{''dns'':
     dns_servers => [''10.100.100.1'']
   }
}

class role::loadbalancer inherits role {
   Class[''dns''] {
     dns_servers => [''127.0.0.1'']
   }
}

node loadbalancer1 {
   include role::loadbalancer
}

I expected resolv.conf to have the 127.0.0.1 address, but it has the
10.100.100.1 address.

Could someone explain to me the rules around parameterized class inheritence.
And if using inheritence to override general use cases for very common
modules is not the way, should all this logic then be put into our
extlookup or something like hiera?


Jos

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On Mon, Feb 20, 2012 at 8:24 AM, Jos Houtman <jos@hyves.nl>
wrote:
> Hi group,
>
> I expect parameterized classes to behave simular to types in relation
> to overrides, but obviously this is not the case.
> Could someone what is should then expect from overriding an parameterized
class.
>
> what I have is:
>
> class dns(dns_servers) {
>  file{''/etc/resolv.conf'':
>      content => template("dns/resolv.conf.erb")
>  }
> }
>
> class role::init {
>   class{''dns'':
>     dns_servers => [''10.100.100.1'']
>   }
> }
>
> class role::loadbalancer inherits role {
>   Class[''dns''] {
>     dns_servers => [''127.0.0.1'']
>   }
> }
>
> node loadbalancer1 {
>   include role::loadbalancer
> }
>
> I expected resolv.conf to have the 127.0.0.1 address, but it has the
> 10.100.100.1 address.
>
> Could someone explain to me the rules around parameterized class
inheritence.
> And if using inheritence to override general use cases for very common
> modules is not the way, should all this logic then be put into our
> extlookup or something like hiera?
Parametrized classes do not behave like resources, so you can''t
override them in an inherited class. In your case, either do not
inherit and declare the class separately, or declare include ntp, and
change class definition to
dns(dns_servers=hiera(''dns_server'')) {...}

Thanks,

Nan

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This is actually filed in Bug #5517 (Accepted) and a few others and has 10 
votes.

http://projects.puppetlabs.com/issues/5517

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On Feb 20, 10:24 am, Jos Houtman <j...@hyves.nl>
wrote:
> Hi group,
>
> I expect parameterized classes to behave simular to types in relation
> to overrides, but obviously this is not the case.
> Could someone what is should then expect from overriding an parameterized
class.
>
> what I have is:
>
> class dns(dns_servers) {
>   file{''/etc/resolv.conf'':
>       content => template("dns/resolv.conf.erb")
>   }
>
> }
>
> class role::init {
>    class{''dns'':
>      dns_servers => [''10.100.100.1'']
>    }
>
> }
>
> class role::loadbalancer inherits role {
>    Class[''dns''] {
>      dns_servers => [''127.0.0.1'']
>    }
>
> }
>
> node loadbalancer1 {
>    include role::loadbalancer
>
> }
>
> I expected resolv.conf to have the 127.0.0.1 address, but it has the
> 10.100.100.1 address.
>
> Could someone explain to me the rules around parameterized class
inheritence.

Parameterized class inheritance is just like non-parameterized class
inheritance.  In fact, it is *exactly* like non-parameterized class
inheritance, including that it provides no mechanism for the
parameters of the superclass to be set when the subclass is declared.

> And if using inheritence to override general use cases for very common
> modules is not the way, should all this logic then be put into our
> extlookup or something like hiera?

My recommendation is to use hiera for all the needs you may now be
addressing via class parameters.  You may find that that also reduces
your interest in class inheritence, but if you still want to use some
inheritence then you won''t need to deal with parameterized base
classes.


John

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